Tropical ideals do not realise all Bergman fans

Every tropical ideal in the sense of Maclagan–Rincón has an associated tropical variety, a finite polyhedral complex equipped with positive integral weights on its maximal cells. This leads to the realisability question, ubiquitous in tropical geometry, of which weighted polyhedral complexes arise in this manner. Using work of Las Vergnas on the non-existence of tensor products of matroids, we prove that there is no tropical ideal whose variety is the Bergman fan of the direct sum of the Vámos matroid and the uniform matroid of rank two on three elements and in which all maximal cones have weight one

Exportación de sedimentos desde cuencas hidrográficas de la vertiente oriental del golfo de Urabá: influencias climáticas y antrópicas

En este artículo se analizaron series de tiempo mensuales de precipitación (mm), caudal (m3/s) y exportación de sedimentos (kton/día) en cuencas de la vertienteoriental del golfo de Urabá. Se analizó la dinámica de la exportación de sedimentos, la relación caudal - exportación y caudal - precipitación. Se infirió el papel de fenómenos atmosféricos estacionales y multianuales (El Niño - Oscilación Sureña, ENOS),y factores antrópicos. Se encontraron variabilidades intra - anuales significativas (ANOVA: p<0.001) consistentes con las oscilaciones de la Zona de Convergencia Intertropical. Correlaciones de Pearson mostraron relaciones directas y significativas (p<0.001). El ENOS no presentó influencia sobre la precipitación. Con aerofotografías se analizó el efecto antrópico en los municipios de Apartadó (1961 - 2005) y Chigorodó (1961 - 2007), y se encontró pérdida de cobertura boscosa del 90%. Las figuras de doble masa reflejaron, al cambiar la pendiente positivamente, a mediados de los 90, que la tasa de exportación de sedimentos fue mayor por metro cúbico de caudal, sugiriendo que hay un efecto antrópico

Characterization of the iron-regulated desA promoter of Streptomyces pilosus as a system for controlled gene expression in actinomycetes

BACKGROUND: The bioavailability of iron is quite low since it is usually present as insoluble complexes. To solve the bioavailability problem microorganisms have developed highly efficient iron-scavenging systems based on the synthesis of siderophores that have high iron affinity. The systems of iron assimilation in microorganisms are strictly regulated to control the intracellular iron levels since at high concentrations iron is toxic for cells. Streptomyces pilosus synthesizes the siderofore desferrioxamine B. The first step in desferrioxamine biosynthesis is decarboxylation of L-lysine to form cadaverine, a desferrioxamine B precursor. This reaction is catalyzed by the lysine decarboxylase, an enzyme encoded by the desA gene that is repressed by iron. RESULTS: The binding of the DmdR (acronym for divalent metal dependent repressor) to the desA promoter in presence of Fe(2+ )or other divalent ions has been characterized. A 51 bp DNA fragment of the desA promoter containing the 9 bp inverted repeat was sufficient for binding of the DmdR repressor, as observed by the electrophoretic mobility shift assay. The desA mobility shift was prevented by neutralizing DmdR with anti-DmdR antibodies or by chelating the divalent metal in the binding reaction with 2,2'-dipyridyl. Binding to the desA promoter was observed with purified DmdR repressors of Streptomyces coelicolor or Rhodococcus fascians suggesting that there is a common mechanism of iron-regulation in actinomycetes. The complete desA promoter region was coupled using transcriptional fusions to the amy reporter gene (encoding α-amylase) in low copy or multicopy Streptomyces vectors. The iron-regulated desA promoter was induced by addition of the iron chelating agent 2,2'-dipyridyl resulting in a strong expression of the reporter gene. CONCLUSIONS: The iron-regulated desA promoter can be used for inducible expression of genes in Streptomyces species, as shown by de-repression of the promoter when coupled to a reporter gene

Genomic variation and population structure detected by single nucleotide polymorphism arrays in Corriedale, Merino and Creole sheep.

THE AIM OF THIS STUDY WAS TO INVESTIGATE THE GENETIC DIVERSITY WITHIN AND AMONG THREE BREEDS OF SHEEP: Corriedale, Merino and Creole. Sheep from the three breeds (Merino n = 110, Corriedale n = 108 and Creole n = 10) were genotyped using the Illumina Ovine SNP50 beadchip(®). Genetic diversity was evaluated by comparing the minor allele frequency (MAF) among breeds. Population structure and genetic differentiation were assessed using STRUCTURE software, principal component analysis (PCA) and fixation index (FST). Fixed markers (MAF = 0) that were different among breeds were identified as specific breed markers. Using a subset of 18,181 single nucleotide polymorphisms (SNPs), PCA and STUCTURE analysis were able to explain population stratification within breeds. Merino and Corriedale divergent lines showed high levels of polymorphism (89.4% and 86% of polymorphic SNPs, respectively) and moderate genetic differentiation (FST = 0.08) between them. In contrast, Creole had only 69% polymorphic SNPs and showed greater genetic differentiation from the other two breeds (FST = 0.17 for both breeds). Hence, a subset of molecular markers present in the OvineSNP50 is informative enough for breed assignment and population structure analysis of commercial and Creole breeds

Evaluación educativa de la implementación de un programa interactivo para la adquisición de conocimientos medioambientales

Para conocer la calidad docente dentro de nuevas metodologías de aprendizaje es importante prestar especial atención a la evaluación, sus pautas, los diseños realizados y el proceso en sí, que junto con los resultados obtenidos nos indican los criterios susceptibles de mejora, así como las áreas fuertes y débiles a considerar para futuras experiencias dentro de la docencia. La evaluación se ha realizado dentro del proyecto“Propuesta metodológica para el aprendizaje autónomo de conceptos medioambientales en la formación de maestros”, que nace con la intención de adecuar la metodología de la asignatura obligatoria Fundamentos científicos medioambientales, por su adaptación en su manera de desarrollo a través de entornos virtuales

Physiology\u27s influence on the thermal comfort of the occupants: A study in Ensenada, Baja California

INTRODUCTION: Thermal environment\u27s adverse conditions can significantly affect the performance, comfort and well-being of people, so this study aims to estimate the thermal comfort range from the cold period in Ensenada city, Baja California: February month, from different levels of metabolic activity: passive, moderate and intense. PURPOSE: This study seeks to identify the relationship between the people thermal perception, their metabolic activity and the physical or psychological sensations involved in the process of adaptation indoors. Thermal sensations are caused by several factors: 1) Physical stimuli of the thermal environment, 2) Activity metabolic, as well as the intensity with which it is performed, 3) Clothing, 4) Experience and 5) Human expectation. METHODS: Data collection was based on the application of questionnaires, which considered physiological, perceptual and environmental characteristics measurements. The study case is located in Ensenada city (temperate-dry bioclimate); with a target population that is within the range of 15-19 years old and 20-24 years old. It was decided to apply the assessments to university students of the Autonomous University of Baja California, who represent 60 % of the statewide student community. RESULTS: Estimated thermal comfort during the cold period resulted from 16.9 °C to 23.9 °C for occupants that exercising passive activity (0.8 met to 1.2 met), from 16.6 °C to 23.9 °C for moderate activity (1.2 met to 1.6 met); and 17.1 °C to 23.2 °C for those who exercised intense activity (2.0 met to 2.4 met). CONCLUSION: According to the aforementioned, it is possible to inform that occupants metabolic activity and, thereby the production of generated internal heat, exerts an influence in the thermal sensation that they perceive from immediate environment

Comparison of five different RNA sources to examine the lactating bovine mammary gland transcriptome using RNA-Sequencing.

The objective of this study was to examine five different sources of RNA, namely mammary gland tissue (MGT), milk somatic cells (SC), laser microdissected mammary epithelial cells (LCMEC), milk fat globules (MFG) and antibody-captured milk mammary epithelial cells (mMEC) to analyze the bovine mammary gland transcriptome using RNA-Sequencing. Our results provide a comparison between different sampling methods (invasive and non-invasive) to define the transcriptome of mammary gland tissue and milk cells. This information will be of value to investigators in choosing the most appropriate sampling method for different research applications to study specific physiological states during lactation. One of the simplest procedures to study the transcriptome associated with milk appears to be the isolation of total RNA directly from SC or MFG released into milk during lactation. Our results indicate that the SC and MFG transcriptome are representative of MGT and LCMEC and can be used as effective and alternative samples to study mammary gland expression without the need to perform a tissue biopsy